Generally speaking, most teaching places are equipped with backboard or whiteboard for the teacher to write down the text or to make explanations. In some occasions, pencils or whiteboard-writing pens are used for writing on whiteboards. But pencils and whiteboard-writing pens often contain volatilizable and poisonous organic solvents, which do much harm to human bodies. In other places chalks are used. The chalk dusts adhere on the blackboard, and with the motion of the eraser, drop down and fly away all around, making the ambient space filled with chalk dusts. This is also very harmful to the teachers and learners, especially, the young children. Since using chalks and common blackboard erasers causes lots of flying dusts, it is not good to the health and inconvenient for teaching, and is often criticized by the teachers.